Canadian Mineralogist
Yol.24, pp. 5l-54 (1986)
RAPIDCREEKITE,
A NEW HYDRATEDCALCIUM SULFATE-CARBONATE
FROM THE RAPID CREEKAREA, YUKON TERRITORY
ANDREWC. ROBERTS,H. GARY ANSELL ANDIAN R. JONASSON
GeologicalSurveyof Canada,601Booth Street,Ottowa,OntarioKIA 0E8
JOEL D. GRICE
Mineral Sciences
Division,NationalMuseumof Natural Sciences,
1026MerivaleRoad, Ottawa,OntarioKiA 0M8
ROBERT A. RAMIK
Departmentof Mineralogltand Geologlt,Royal OntarioMuseum,100Queen'sPark, Toronto, OntarioMSS2C6
ABSTRAcT
un bon clivage{100} et un clivageparcreekiteprdsente
et2.239(calfait {010}.Sadensit€
estde2.2l(l) (mesur6e)
sousl'ultraviolet.Elleest
cul6e);ellen'estpasfluorescente
positive,
biaxiale
a 1.516(1),
B 1.518(l),7 1.531(l),2V"
(mesur6)
43" ; l'orientationdeI'indi45(3)",2Vr(calcul6)
catriceest:X = c, Y= a, Z = b. Leshuit raieslesplusintensesdg diagrammede poudreobtenupar diffractionX [d
en A(t)(afDl sont les suivantes:7.78(100)(200),
I ), 3.I I (80)(421,40q,
r 1,400,23
4.3| Q0)Q2r),3.88(70X3
6r), 2.s55(s0)(r42,322) eI
2.9t7(50)(43
t), 2.797(60',)(r
i la microsonde
082).Lesanalyses
1.899(50)(303,580,233,
* analyse
des
thermogravim€trique
et I'analyse
6lectronique
gaz6misCIGA-EGA)donnent:CaO36.3,SO326.1'CO2
(enpoids).Le nomrap14.0et H2O23.6,total 100.090
pelleI'endroitoir la nouvelleespdce
a 6t6trouv6e.
Rapidcreekite,ideally Ca2(SO/(COr1.4gr6, is a new
secondarymineral speciesfrom the Rapid Creek area,
northe.rnYukon Territory. It occurson beddingplanesand
joint surfacesof a quartz-rich iron formation, as crystalline coatingsand spraysof white to colorlessacicular crystals. The symmetry is orthorhombic, space gogp Pcnb,
with a 15.49(l), , 19.18(l), c 6.157(4)A, a:b:c
0.808:1:0.321,Z = 8. Individual crystalshavea maximum
len&h of 2 mm and are elongate[001], with forms {010}
broad and {100}, {001} minor. The streakis white; lustre
vitreous; brittle, fracture splintery; Mohs hardness 2;
cleavage{010} perfectand { 100} good; D(meas.)2.21(l),
D(calc.) 2.239g/cms; nonfluorescentin ultraviolet light.
Rapidcreekite
is biaxialpositive,cr 1.516(l),0 1.518(l),r
sulfate
min6rale,rapidcreekite,
1.531(l), 2Z* (meas.)45Qr',2Zxk*.lc.) 4", indicatrix Mots-clds:
nouvelleespbce
Yukon,Rapid
orientation X = c, Y=a, Z=b. The strongeliteight lines
et carbonate
de calciumtetrahydrate,
chimique.
de rayonsX, composition
in the X-ray powder-diffraction pattern [d in A(I) (hkl)] are
Creek,donndes
7.78(100x200), 4.3r(70)Q2r), 3.88(70X3
l 1,400,23
l),
3. l I (80X421,002), 2.9r7(s0)(43r), 2.797(60)(l61),
INtnooucrtoN
2.555(s0)(142,322)and 1.899(50)(303,580,233,082).
Microprobeanalysesand TGA-EGA gaveCaO 36.3, SO3
The Rapid Creek - Big Fish River area of the
26.1,CO214.0and }J2O23.6,sum [email protected] wt.Vo.The name
refers to the general locality.
northern Yukon Territory is best knpwn for the
Keywords: new mineral species,rapidcreekite,calcium sulfate carbonatetetrahydrate,Yukon, Rapid Creek, Xray data, chemicalcomposition.
SOMMAIRE
La rapidcreekite, dont la formule iddale est Ca2(SOa)
(CO3).4H2O,estune nouvelleespbcemin6ralesecondaire
d6couvertedansla r€gion du ruisseauRapid, dansle Nord
du Yukon. On la trouve sur les plans de stratification et
de s€parationd'une formation de fer riche en quartz, sous
forme d'enduits ou de gerbesde cristaux aciculairesblancs
ou incolores. La symdtrieestorthorhombique, grolrpe spatiaTPcnb, a 15.49(1),, 19.18(1),c 6.157(4)A, a:b:c
0.808:l:0,321,Z: 8. Lesmonocristaux
ont, tout au plus,
2 mm de longueur et sont allongds[001], la forme {010}
estlargeet lesformes{l@} et {001} sont eftoites.Cescristaux sont fragiles, d trait blanc, 6clat vitreux et cassure
esquilleuse;de duretd 2 sur l'4chellede Mohs. La rapid-
unique assemblages
of phosphatemineralsthat occur
in a sequenceof Lower Cretaceous(Albian) ironstones and shales. However, recent surfaceweatheringhas resultedin the formation of many
secondarysulfate and carbonateminerals,most of
which havenot beenreportedto date. Among these
are aragonite,nesquehonite,dypingite, hydromagnesite, gypsum, hexahydrite, halotrichite, epsomite,
jarosite, natrojarosite and diadochite (a sulfatephosphate).
Rapidcreekite,ideally Car(SOn)(CO).4HrO,is a
new mineral speciesfirst encounteredin 1983,and
to date found only at one locality along the valley
of a tributary (unofficially, CrosscutCreek)of Rapid
creek, at latitude 68"33'45',N, longitude
136"47'30'W. Rapidcreekiteoccursas a secondary
phaseon dilated joint-surfacesand beddingplanes
in a blocky, quafiz-rich bed in the sideritic ironformation. Minor amounts of glpsum and aragonite
51
52
THE CANADIAN MINERALOGIST
are associatedwith rapidcreekite,and kulanite is slowly in heavyliquids, a measureddensityof 2.21(l)
g,/cm3was obtained, in reasonableagreementwith
found on the holotype specimen.
The mineral is namedfor the generallocality; both the calculated density of 2.239 g/cm3 for
nameand mineral havebeenapprovedby the Com- CalSo)(Co)4}J2o.
rnission on New Minerals and Mineral Names,
Optical measurementswere made on a spindle
I.M.A. The holotype specimen,consistingof a few stageusing sodium light O 589 nm). Rapidcreekite
grams of material on matrix, is housedin the Sys- is biaxial positive, cu 1.516(l), 0 1.518(l) and y
tematic ReferenceSeriesof the National Mineral Col1.531(1).The measured2V*is 45(3)",closeto the
lection, at the GeologicalSurveyof Canada,Ottawa, calculatedvalue of 43" . Optical orientation is X: c,
under cataloguenumber U346. Addiiional speci- Y:a and Z:b.
mens of rapidcreekite are preservedat the GeologiCRYSTALLOGRAFHY
cal Survey and at the Mineral SciencesDivision,
National Museum of Natural Sciences,Ottawa.
Precessionsingle-crystalstudies employing Mo
radiation of two crystalfibres showthat rapidcreekite
Pnvsrcal ANDOPTICALPRoPERTIES
is orthorhombic, spacegrovp Pcnb, with measurgd
Rapidcreekiteoccursmost commonly as radiat- unit-cellparametersa I 5.45, b 19.16and c 6. I 65 A.
ing spraysof white to colorlessacicularcrystals,in The levels collected are hle0-hk2, 0kl-Skl and
both isolatedclustersand pervasivecoatingson rusty- h\l-h\l. The X-ray powder-diffraction data (Table
l) were^refinedon l8 reflectionsbetween3.005and
weathering quartz-rich iron formation. Individual
crystalsare colorless,transparentand acicular, elon- 1.655A for which unambiguousindexing was posgate parallel to [001], with forms {010}broad and sible, basedon precessionsingle-crystalfilms. The
tl00l, [001]minor (Fig. 1), and approach2 mm in refined unit-cell par4meters arei q 15.49(l), b
maximum length. The coarsermaterial has a length- 19.18(l), c 6.151(4)A, V tgZg.Z 43, and q:b:c
to-width ratio of about 50:1. Bundlesof individual 0.808:I :0.321. The strongestdiffraction-lines are
crystals appear lath-shaped. The mineral is brittle closeto thoseof gypsum,but the completepowderwith a white streak, vitreous lustre, splintery frac- pattern is significantly different from any mineral
ture, and a Mohs hardnessof 2. Observedcleavages ofthe gypsumgroup. However, the powder data are
are [010] perfect and {100} good. Rapidcreekiteis very similar to the [email protected].
nonfluorescentunder both long- and short-wave 29-294) described by Walenta (1972) from the
ultraviolet radiation. Although the mineral dissolves Johann mine, Wittichen region, Germany. There
seems little doubt that this latter mineral is the
arsenateanalogueof rapidcreekite.This is further
supported by the near-identity of their optical
properties.
TABLE I. X.RAY POVDER-DTFFRACTION DATA FOR RAPIDCRBEKITE
r*
Ftc. l. Scanning-electronphotomicrograph of rapidcreekiteshowingtypical habit of crystals.Lenglh of bar
is l0 rn..
a,i .*.
100
20
J
l0
70
7.7t
5.tt9
4.91
4.6t
s.3l
70
3.88
40
).66
40
3.41
2b
3.72
t0
,.ll
20
50
1.005
2.917
1('b
2.871
60
2.797
1@
2.743
30
2.61
50
2.555
20
2.tt49
10b
2.)a6
a,i."t".
7.75
,.48
tt.9l
4.67
4.3t
3.tt
t.a7
,.85
3.64
3.66
3,40
t.23
3.20
).10
,.a|
3.0t2
2.917
2.t80
2.a61
2.79t
2.754
2.730
2.659
2.555
2,549
2.444
2.398
2,t91
2.370
114.6 mm Debyq.Scher.s Fsds
7tA), b=br€d llne
ocukGl.r4l
hkl
200
ln
l2l
2ll
Z2l
3lt
r.00
231
l4l
321
24r
4ll
060
421
0m
251
431
122
2C2
l5l
351
l?2
52r
142
122
t32
080
4t2
lto
oA .*.
td
2.3t2
30
5
t0
20
2.r7t
2.@l
2.q70
10
2.*4
5
40
40
2.0@
1.986
1.9'
50
t'6"
l0
5
L.E3t
1.786
l0
t.76t
t.7t0
l.68rr
t,655
@msa, Cu radatlon Ni tllt€
irde:cd eith o 15.49.b l9.IE sd c 6.lr7i
oi *t".
2.t16
2.211
2.245
2.2ta
2.212
2,170
2.6t
2.071
2.Ot7
2,019
2.035
2.010
l.9tt
1.949
1.907
1,E96
1.89i
1.a92
l.a,
1.7a7
1.766
1.75a
1.757
l.7ll
L6Ei
1.656
hk'l
342
371
t'l
2
l8l
5t2
561
7ll
072
4t0
r03
740
5tt2
Dr
303
'80
zrt
@2
243
491
722
652
6t0
503
742
4l!l
RAPIDCREEKITE, A CALCIUM SULFATE-CARBONATE
FROM RAPID CREEK
2000
1000
53
too
c
80
.9
(tt
.9
E
;60
c
qt
1E - ' 4 0
o
bzo
o-
4000
15 0 0
500
W a v e n u m b e rc m - r
Ftc. 2. Infrared-absorptionspectrumfor rapidcreekite.
CHEMISTRY
Rapidcreekite was analyzed by means of a
Materials Analysis Company (MAC) electron
microprobe equipped with a KEVEX energydispersion spectrometer (M. Bonardi, analyst).
Accelerating voltage was 20 kV with a sample current of l0 nA as measured on kaersutite. To
minimize sample degradation and compositional
changedueto electronbombardment,a slightly defocusedbeam was used over a counting time of 100
seconds.
An energy-dispersionscrmon a hand-picked crystal aggregateindicated that Ca and S are the only
elementspresent with atomic number gleater than
10. Subsequentenergy-dispersion
analysesweremade
usinggypsum(NMC 17182,Moose River, Ontario)
as a standard. Analytical data were corrected with
EDDI, an in-houseenergy-dispersiondata-reduction
program written by G.J. Pringle. TGA-EGA
@volved Gas Analysis) determinationsfor H2O and
CO2 were made on 3.605 mg of sampleusing the
Mettler thermal analyzer and integrated massspectrometerat the Royal Ontario Museum.Major
peaksat 230",660" and 1105'Careascribedto the
evolution of H2O, CO2 and SO3,respectively.
A 25 mg sampleof rapidcreekitewas checkedfor
the presenceof other anions using a Dionex anion
chromatograph. Results of one analysiswere: F0.09,Cl- 0.03,PO4r 0.07and NO3-0.15weightgo,
most likely attributable to contamination.
CombinedanalyticalresultsgaveCaO 36.3, SO3
26.1, CO2 14.0 and Il2O 23.6, total 100.00weight
90. Assuming S= I , the empirical formula for rapidcreekite is Ca,.er(SO)r.00(COJo.e8.4.02H2O
or,
ideally, Caz(SO+XCO).4HzOwith Z=8. The
mineral dissolvesslowly in 1090HCI with slight effervescence.
Calculationsusing the Gladstone-Dalerelationship yieldedKc = 0.232and Kr : 0.233for constants reported by Mandarino (1981); hence
l-(Kp,/Kd is 0.0043,indicating superior compatibility (Mandarino 1979).
An infrared-absorption analysis@ig. 2) indicates
that the formula CaISO)(CO3).4H2O is to be
preferred over Ca2(SO)(HCO3XOH).3H2O.No
positive evidencewas found for the presenceof
HCO3- or OH- in rapidcreekite.However, a crystalstructure determinationwould be necessaryto verify
the correct formula.
AcrNowrsncEMENTS
The authors thank J.L. Jambor, CANMET, for
the determination of the specific gravity, V.H.E.
Rolko, CANMET, for the infrared-absorption
study, D.A. Walker, G.S.C., for the SEM photomicrograph,M. Bonardi, G.S.C., for the electronmicroprobedata, W.G. Young, G.S.C., for drafting Figure 2, A.I. Maclaurin for Dionex analyses
and G.W. Robinson, N.M.C., for helpful discussions. Logistical support in the field was supplied,
in part, ty the Polar Continental Shelf Project
@nergy,Mines and Resources,Canada)and by the
Inuvik ScientificResourceCentre(Indian and Northern Affairs), whose assistance is gratefully
acknowledged.We thank PeteJ. Dunn, EugeneE.
Foord, Antlony R. Kampf and Robert F. Martin
for critical readings of the manuscript.
THECANADIANMINERALOGIST
54
WALE*re, K. (1972):The secondaryminerals of the
Co-Ni-Ag-Bi-U oreveinsin theWittichenregion,
23,279'329 (ia
(1979):
relaThe
Gladstone-Dale
Meroanno, J.A.
I:ntral Black Fotest. Aufschluss
German)'
tionship. III. iome'general applications.Can.
Mineral.17.71-76,
RsFERENcss
(1981):The Gladstone-Dalerelationship.IV.
fne iompitiUility conceptand its applicatioi. Can.
Minerql. 19, M1450.
ReceivedJune 27, 1985,revisedmanusoipt accepted
September4' 1985.